In the analysis and study of many types of particles such as blood particles, the particles are suspended in a liquid medium. The medium is then introduced into a particle analyzing device of the general type described and claimed in U.S. Pat. No. 3,259,842 which issued July 5, 1966 to W. H. Coulter, et al., and which is assigned to the Assignee of this invention. The particle analyzing device described in the said U.S. patent employs a Coulter type particle detector wherein a particle in the suspension medium will modulate the current flow or electric field in an aperture to produce an electrical pulse as the particle passes through the aperture. The electrical pulse is then coupled to a pulse processor where characteristics such as the pulse amplitude are analyzed in order to yield certain information regarding particle size. The pulse also can be counted in order to ascertain particle concentration.
Although particle analyzers of the Coulter type noted above have enjoyed great success for a number of years, such an instrument takes an appreciable period of time, relatively speaking, to process each pulse. For example, processors currently available can process a pulse in 50 to 100 microseconds. If there is a high concentration of particles in the suspension medium, the Coulter type particle detector may develop pulses faster than they can be processed by the pulse processor. Furthermore, even with low particle concentrations, pairs or groups of particles can arrive in rapid succession due to an uneven dispersion of particles in the fluid, causing pulses to be developed faster than can be processed by the pulse processor.
If each pulse must not only be processed but counted by the pulse processor in order to statistically analyze the particles accurately, the pulses developed by the particle detector must be stored or "frozen in time", until they can be processed by the pulse processor. If each pulse is stored for a predetermined period of time while the processor is processing a preceding pulse, the number of pulses stored will not be substantially decreased when the rate at which the pulses are produced decreases. Furthermore, when the rate at which pulses are developed increases to a point greater than the speed at which each pulse can be processed, the number of pulses in storage will increase until the full capacity of the storage device is utilized.